This proposal involves a study of children's social development as measured in terms of patterns in social behavior and performance on assessments of social reasoning. The aim of the study is to develop an integrated theoretical perspective, based on the metaphor of "planfulness", which allows behavior patterns to be meaningfully related to social reasoning performance. The study focusses on social interaction among initially unfamiliar children aged five, seven, and nine who are brought in same-age groups of six to a playroom laboratory for twelve after-school playgroup hours, during which they develop nascent social relations. Behavioral data is gathered through use of an audiovisual surveillance system which incorporates individually accessible audio tracks for each child and three separate camera views of playroom activity, resulting in a set of behavior records of quality unparalled in past work. Interview assessment of social reasoning includes a procedure in which children are shown films of themselves and asked to make judgments about their social interactions, another novel and important procedure.